The use of biocides in mineral slurries is well known. Biocides are used in mineral slurries to inhibit bacterial growth. Typically, biocides are added both during the manufacturing process and as preservatives in the final product. The product selection and dosage is normally based on extensive laboratory analysis to measure product efficacy and interactions with other slurry components. Additionally, regulatory, safety and customer requirements also impact the choice of biocide.
There are a limited number of biocides with the appropriate EPA and FDA clearances for use in mineral slurries to inhibit bacteria growth. These products primarily include glutaraldehyde (Glute), 1,2 benzithiazolin-3-one (BIT), tetrahydro-3-5-methyl-2H-1,3,5-thiadizine-2-thione (thione or dazomet), isothiazoline (Iso), bronopol (BNPD), orthophenyl phenate (OPP), or 2,2-dibromo-3-nitrilopropionarnide (DBNPA).
A particular one of these biocides is sold under the name BCS 3243which is tetrahydro-3,5-dimethyl-2H-1,3,5-thiadiazine-2-thione, which is also known in the industry as thione or dazomet (hereinafter thione) CAS #53-74-4 and EPA Reg. No. 1448-103-82760. This material is designed to preserve clay slurries, adhesives, coatings and high viscosity suspensions. Thione is sold in dry, caustic based solution and water based emulsion forms. For preservation of slurries and high viscosity suspensions, thione is typically added at a point in the processing system where there will be sufficient time and agitation for good mixing and dispersion. Preferred amounts are at levels of 0.04-0.45%, by weight, based on the total formulation in slurries of kaolin, starch, clay, calcium carbonate, or titanium dioxide. Thione also has applications in paper coatings; high viscosity suspensions (e.g., polymers, silica-polymer combinations); polyvinyl alcohol/polyvinyl acetate-based adhesives; starch-based adhesives; in oilfield applications and dextrin-based adhesives. The exact amount of material to be added for the preservation of any given formulation will depend on the components and local storage time and conditions. Dosage rates are normally determined by actual tests.
These known biocides have numerous limitations as they can be sensitive to slurry pH and temperature, they can impact quality, they have odor and can have high VOC's, the efficacy can be insufficient, and they can be expensive. Glutaraldehyde can be problematic because it is hazardous to handle and has environmental concerns. Moreover, it contains aldehydes, is the least cost efficient biocide, and is odiferous. BIT and ISO are also limited in applications based on slurry pH, interactions with other slurry components, and temperature. Bronopol is susceptible to high process temperatures, pH, and interaction with slurry components. Thione is a good broad spectrum biocide and is versatile but has limited application because it creates odor and has other health and safety issues due to the presence of formaldehyde.
There is a need for additional and more versatile biocides to address changing slurry formulations, regulatory constraints, slurry interactions, efficacy, odor, and be able to mitigate many of these problems.